1. Field
The present disclosure relates to the field of communications, and in particular to a monitoring apparatus for an optical signal to noise ratio, a signal transmission apparatus and a receiver.
2. Description of the Related Art
No matter in a conventional direct detection optical communication system or in a coherent optical communication system, an optical signal to noise ratio (OSNR) is a quantity that may be directly associated with the system performance. Hence, attention has been paid to the study of the monitoring technology of the OSNR.
A conventional measurement method based on the definition of OSNR relies on such conditions as that a noise power spectrum is flat and a band containing a noise but containing no signal exists in the spectrum. As increase of an optical communication capacity, a transmission length and a transmission rate of the coherent optical communication system are largely improved. More optical nodes will result in larger fluctuation of a spectral shape of the noise, and an assumption of noises being evenly distributed on the spectrum will face larger challenges. And in the same time, as channel intervals are largely reduced, finding a band where signals may be neglected to measure noise power becomes an impractical subject. Hence, measurement of OSNR in a coherent optical communication system becomes a new hot spot of studies.
In a practical communication system, besides noises of a transmission link itself, noises introduced by a nonlinear effect are further included. Wherein, the noises include noises introduced by an intra-channel nonlinear effect and noises introduced by an inter-channel nonlinear effect. In practical OSNR monitoring, when the noises introduced by the nonlinear effect cannot be excluded, an estimated value of the OSNR will be relatively low. In order to alleviate interference of the nonlinear noises on the estimated value of the OSNR, an existing method is to nonlinearly compensate for received signals in a receiving end.
It should be noted that the above description of the background is merely provided for clear and complete explanation of the present disclosure and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background of the present disclosure.